The present invention is directed to stabilized compositions of particulate activated carbon and the use of such compositions to adsorb contaminants from soil and groundwater.
Activated carbon is commonly used as a sorbent medium for removing organic and inorganic contaminants from water. It is used in treatment systems to detoxify industrial process water, as well as in pump-and-treat systems for above-ground treatment of contaminated groundwater. In use activated carbon is typically manufactured and used in granular or powder form whereby the particulate is loaded into fluid- or fixed-bed treatment systems or dispersed or distributed over the area subject to contamination.
The in situ (in place) application of activated carbon to soil and groundwater allows for the capture or immobilization of contaminants from groundwater via sorption onto the carbon. This inhibits the migration of a contaminant plume and lowers the risk of damage to human health or ecological systems. Exemplary prior art teachings of carbon-based compositions for use in environmental remediation include the following references:
U.S. Pat. No. 4,664,809, issued May 12, 1987, to Fenton, entitled GROUNDWATER POLLUTION ABATEMENT, discloses drilling of wells in the ground and injecting a sorbent for contaminants into the path of groundwater plume, in order to stop the plume. Such reference further discloses the use of activated carbon as a sorbent and the addition of stabilizing substances to sorbent slurries.
In the name of Kopinke, F.-D.; Woszidlo, S.; Georgi, A., European Patent Application EP 1462187 A2, filed Mar. 2, 2004, “Verfahren zur in-situ Dekontamination schadstoffbelasteter Aquifere,” discloses a process for in-situ decontamination of polluted aquifers—by injection of colloidal carbon. Such reference discloses that a charcoal particle size <10 microns is optimal and that ionic strength inhibits colloid transport. The objective of the invention is to increase distribution of carbon colloids in subsurface by flushing with deionized water or raising pH of aquifer.
Georgi, A.; Schierz, A.; Mackenzie, K.; Kopinke, F.-D., Terra Tech, 2007, 16, (11-12), 2-4. “Mobile Kolloide. Anwendung von kolloidaler, Aktivkohle zur In-Situ-Grundwasserreinigun, (in German) also refers to aquifer treatment with colloidal activated carbon and that a 0.1 to 10 micron activated carbon particle size is needed for stability and mobility. The optimal particle size is disclosed as 0.5 to 2 microns. Moreover, such reference teaches that humic acid and carboxymethylcellulose are stabilizers of activated carbon colloids and can have a max loading of <10% on carbon.
Mackenzie, K., et al.; Water Research 2012, entitled “Carbo-iron—An Fe/AC composite—As alternative to nano-iron groundwater treatment” and supporting information is a paper teaching the use of “carbo-iron” an activated carbon material that has embedded iron metal particles for contaminant treatment. The carbo-iron is comprised mostly of activated carbon and behaves similarly to activated carbon as a colloidal material. Such reference discloses that max loading of CMC onto carbo-iron is 7% w/w and that no further stabilization benefit occurs above 5% w/w loading of CMC.
The teachings of all the aforementioned references are incorporated herein by reference. Notwithstanding their respective teachings, however, there are significant limitations regarding the use and efficacy of in situ activated carbon treatments. In particular, as a solid powder or granular material, activated carbon cannot distribute through soil to reach areas of contaminated water. Instead, it must be applied in a trench to treat water passing therethrough, or must be injected as a slurry which has limited or no mobility in the aquifer. This lack of mobility causes the cost of treatment to be very high, whereas the contact with contaminated water remains quite low. The high cost is primarily due to the large number of application points required to thoroughly treat a contaminated area.
To facilitate treatment of contaminated groundwater, it is desirable to have a form of activated carbon that can transport effectively through an aquifer to reach contaminated zones while remaining highly sorbent toward contaminants.
The prior art Georgi (2007) and Mackenzie (2012) references referred to above disclose that sodium carboxymethyl cellulose (a polyanionic polymer) stabilizes colloidal activated carbon against settling. It also has some effect to increase transport of activated carbon through soil and groundwater in situ. As the carbon contacts the contaminated groundwater, contaminants are sorbed out of solution and onto the carbon particles. Carboxymethyl cellulose-stabilized colloidal carbon can also transport somewhat in the aquifer, but is destabilized and deposited by ionic strength of the water (Kopinke 2004).
It is therefore desirable to have improved methods and compositions that will distribute colloidal activated carbon much further in the subsurface than simple carboxymethyl cellulose. It is likewise desirable to provide such a composition of colloidal activated carbon that is of simple formulation, easy to deploy, is substantially effective at adsorbing contaminants from soil and groundwater, and is further substantially more effective in becoming dispersed and capable of being quickly and effectively deployed over a greater area of volume of soil and groundwater than prior art activated carbon compositions and methods of using the same for environmental remediation.